Enhanced visibility heat alert safety device for hot surfaces

ABSTRACT

A hot-button type heat alert safety device attachable to a surface, such as metal or glass, for warning individuals that the surface is hot, comprising a thermochromic composition, a button-shaped container for housing the composition, having a convex face, the convex face overlying said composition and the container being transparent in at least a portion of the container overlying the thermochromic composition. The thermochromic composition is designed to undergo and maintain a readily perceptible color change whenever the temperature of the hot surface exceeds a predetermined temperature and reveal a heat warning symbol underneath the thermochromic composition which communicates that the surface is dangerously hot, the heat warning symbol being substantially visible through the convex face of the container.

Priority Information

This patent application claims priority from and is acontinuation-in-part patent application of U.S. patent application Ser.No. 09/788,594 previously filed by Applicant and Inventor William S.Lerner on Feb. 21, 2001 and which is presently pending and incorporatedherein by reference in its entirety. This patent application also claimspriority of and is a continuation-in-part patent application of U.S.patent application Ser. No. 10/238,348 previously filed by ApplicantWilliam S. Lerner on Oct. 9, 2002 and which is presently pending andincorporated herein by reference in its entirety. This patentapplication also claims priority of and is a continuation-in-part patentapplication of U.S. patent application Ser. No. 10/612,315 previouslyfiled by Applicant William S. Lerner on Jul. 1, 2003 and which ispresently pending and incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to safety devices used in cooking or otheractivities involving hot surfaces, and in particular it relates tosafety devices which alert someone that the surface of a stove or otherappliance or device is too hot to touch. The present invention alsorelates to detachable heat alert safety devices for any hot surface.

BACKGROUND OF THE INVENTION

With respect to stoves and related appliances, various kinds ofstoves—electric, gas, smooth cooktop using glass or metal tops—andtoaster ovens are well known to be used for heating food. In addition,“mobile stove-type appliances” such as hot plates and warming trays arewell known to be used for heating food. Each of these kinds of stovesand “mobile stove-type appliances” present a safety problem since theheating elements of the stove are hot during the cooking process andremain hot well afterwards. During the cooking process, the safetyproblem caused by touching the heating element is mitigated somewhat byvisual inspection of the stove. With a gas, electric or smooth topstove, for example, the presence of a pot or other utensil on top of thestove might alert someone to the fact that the stove appears to be inuse for cooking and therefore too hot to touch. Even the presence of apot or other utensil is not a reliable clue, however, since people tendto leave tea kettles on their stove perpetually. When the cookingprocess has ended, however, it is generally impossible to detect thatthe heating elements of the stove remains hot and would burn the skin ofanyone who touched them. There is no visual or other clue that the stoveis hot.

To some degree, adults have developed an inherent caution whenapproaching stoves because of their experience and knowledge in dealingwith such safety problems. This inherent caution, however, does notobviate the need for a device that warns the adult when touching thestove would be dangerous. Moreover, children, and particularly youngchildren, usually have not developed such a watchfulness and there haslong been a need for a device that can prevent burn accidents tochildren who may inadvertently touch a stove that is hot, especiallywhen the stove remains hot well after the cooking process has ended.

Furthermore, the reduction in the size of modern kitchens has led theoccupants of modern apartments to make use of the stove as an extensionof the counter top adjacent the stove as a resting places for largeitems that have been carried into the kitchen area. An example of suchitems is heavy bags of groceries brought into the kitchen. There is anurge to set the bags down on the nearest flat surfaces, which may be thetop of a stove adjacent a counter top. This is particularly true forthose stoves that are smooth on top, such as smooth cooktops. Ingeneral, the top surfaces of modern kitchen stoves are increasinglyflat, especially the top surfaces of smooth cooktops. These factors haveonly increased the danger to adults when the top surfaces of stoves areused as a resting place for packages, such as groceries brought into thekitchen.

Smooth cooktop stoves presently are also dangerous if touched on theirtop surface when they are still hot, even after use. These smoothcooktop stoves, or “smoothtops” as they are sometimes called, utilize asthe heating element separate areas on the top surface of the stove (atthe same location that gas stove would have burners) which are made ofglass. Under each area, usually circular, is a strong light source, suchas a halogen lights. The light source projects the light upward to thesurface area of the smoothtop's heating element—the glass area on thetop surface of the stove. Since the glass area is coated on its bottomwith a dark coating, when the light strikes it, the heat from the stronglight is absorbed by the glass area and these glass surfaces form eachheating element of the stove.

Another variation of the smooth cooktop is the use of a “ribbon heatingelement” where the smooth glass surface is heated by a coiled electriccircuit called a “ribbon element” just underneath it instead of by ahalogen light source. The heat is transmitted directly upward so thatonly the heat element itself gets hot and the rest of the cooktopsurface remains cool. In some cases, the ribbon heating element also hasanother feature whereby the heating element is made of two concentriccircles so that the option exists of two sizes of the heating element tomatch the two different sizes of the pans that need to be heated. Thisnew technology does not solve the problem of warning adults and childrenthat the heating element should not be touched when the cooking processhas ended. If anything, it generates the additional hazard that someonecan be lulled into touching the heating element after thinking theheating element is cool since the surface right adjacent to it is indeedcool.

Some of these problems have been addressed in earlier patents, throughuse of thermochromic inserts or overlays. Thermochromic materials arethose such as some liquid crystals which change color when passingthrough a given temperature range, and are now familiar from use ininexpensive items, like temperature indicating refrigerator magnets orstick-on aquarium thermometers.

These devices however still suffer from some drawbacks. Flat appliablethermometers tend to be made of plastic, and would melt or be destroyedat the temperatures reached by a kitchen oven. Higher temperaturechemical temperature indicating systems are known, such as thesemiconductor cadmium sulfide, but must either be included as inserts inoriginal equipment manufacturing, or fired on as a vitreous ceramic.Materials which are both capable of resisting high temperature and aretransparent, or which are themselves thermochromic, are brittle, and sounsuitable for forming in thin flat removable displays, which makes itdifficult to attach these materials to an existing surface, the wayrefrigerator magnet thermometer is attachable.

In an additional drawback of the prior art, flat indicators, embedded inor applied to a flat surface, are necessarily only usefully visiblethrough a limited viewing angle. It is readily shown throughtrigonometry that if an observer is offset an angle α from the verticalor normal to a surface, which offset is also referred to as the angle ofincidence, the apparent area of objects on the surface will be reducedby a factor of cos(α): A′ =Acos(α). For example, if an observer isoffset 60° from the vertical, i.e., at a 60 degree angle of incidence,viewing a surface from 30° to the surface itself, the apparent size ofobjects on the surface is reduced by cos(60)=½. For an observer at anangle of incidence of 80° the apparent size has shrunk to less than 18%of the actual size; and at 85° apparent size is less than 9% of actual.An angle of incidence approaching 90° from the vertical is known as agrazing angle. At grazing angles α flat indicator on the surface clearlyapproaches zero apparent area, and is completely invisible to theobserver.

A second problem that arises from looking at something at an angle ofthe line of sight is specular reflection. Specular or mirror reflectionis the reflection of light rays hitting a flat surface with a reflectedray having an angle of incidence equal to that of the incident ray. Formost surfaces specular reflectance increases with angle of incidence, sothat more ambient light is reflected to a viewer at larger angles ofincidence of the line of sight. This effect wipes out the contrast of adisplay, so that the display cannot be read at large angles, even if theapparent area of the display were otherwise large enough. Depending onthe type of materials used, the loss in visibility at a given displayangle may be worse than that predicted by apparent area alone. Liquidcrystals for example show a contrast with background notably affected byviewing angle, and readability of a liquid crystal display may bedegraded at lower angles of incidence than other kinds of display.

In consideration of these two effects, loss of apparent viewing area andincrease in specular reflection, flat warning devices are mainlysuitable for surfaces usually seen from small angles of incidence.Examples of such surfaces are vertical surfaces near eye-level, like adoor of a cabinet mounted oven, or horizontal surfaces significantlybelow eye-level, like a stove top surface considered in relation to atypical adult height.

However, for a child an ordinary stove top may be near or even above eyelevel, while small hands can nonetheless reach over the top of a stoveto touch dangerously hot surfaces. Similarly, even for an adult somevertical surfaces such as an oven door, may be below eye level, andhence only visible at a large angle of incidence. This would occur whilea user is standing at the stove and reaching down to open the oven door.A flat indicator therefore will not be prominent or attention getting inthese situations, and may even be invisible to a user.

With respect to toaster ovens, because of the mobility of the unit thedanger of touching the window of a toaster oven exceeds that of thetypical immobile oven. The toaster oven can be placed on a counter topor other portion of the kitchen not directly in the “cooking center”.Consequently, an adult and especially a child, or the elderly, is notlikely to remember not to touch a window of a toaster oven when it isoff (soon after it had been on). In addition, the door of a toaster ovencan be left open and jut out further toward someone in the kitchen.

Presently, in order to address the danger of touching a hot “smoothtop”stove, such stoves generally have several light indicators, each onecorresponding to each heating element, all located in small onerectangular area on the surface of the cooktop. The light indicatorsremain lit for a certain length of time after the stove's heatingelement is turned off in order to deter someone from touching theheating element when it is still hot, although “off”. Unfortunately,this attempt to address the danger of touching a hot stove of the smoothcooktop variety is insufficient as a warning system (putting aside thefact that the light indicators are designed only for the smooth cooktopvariety stoves to begin with and not for gas and electric coil stoves).

A quick glance at the group of light indicators would not be sufficientto warn the average adult, no less children or the elderly, that aparticular heating element is too hot. This is because the group oflight indicators do not immediately tell someone which heating elementscorrespond to which light indicators. At a minimum, several seconds ofconcentration are needed in order to determine from the light indicatorsthat are “on”, which heating elements are too hot to touch. Many adults,and certainly most children, cannot afford those seconds of deductionsince their desire to touch the stove is immediate. In addition, anadult carrying groceries into the kitchen and looking for a counter topto place them on or a child running into and playing in the kitchen areeven less likely than the average adult or child to take the time toengage in a several second thinking process. Accordingly, the child orthe adult will be inadequately warned about the danger of being burned.With this in mind, it is no surprise that a 1997 industrial designexhibit at the Cooper Hewitt (Smithsonian) in New York demonstrated thatover 69% of adults can not match the control knob with its correspondingburner (i.e. heating element) on a stove.

There is also not presently known any effective warning method for thevertical surfaces of oven windows, including the windows of wall ovens,regular ovens and toaster ovens, and especially when such verticalsurfaces are not at or near eye level for a user, as mentioned above.This is particularly important since when the oven is turned off, theoven window remains very hot even though it appears that everything isoff.

While devices that make use of liquid crystal compositions are known toindicate the surface temperature of an appliance, these devices are notdesigned to warn someone of the danger of touching hot stoves. Forexample, U.S. Pat. No. 3,827,301 to Parker discloses an apparatus forindicating the temperature of a surface of an appliance. It has a firstportion in contact with the appliance surface or connected by copperwires or heat pipes to the appliance surface. It has a second portion, apoor heat conducting member in heat exchanging relationship to theambient environment, that has bands of liquid crystal material extendingaway from the first portion thereby creating a temperature gradientextending away from the surface of the appliance. Devices such asdisclosed in Parker that provide temperature determinations are notadequate for instantly warning a child or even an adult that the heatingelement of a stove is too hot to touch for one thing becausequantitative temperature determinations are inadequate to provide theimmediate warning that is necessary. Moreover, the device of Parker andother liquid crystal compositions are not specifically suited to bemanufactured as part of a stove. In addition, these devices are notsuitable as attachments to stoves and certainly not as attachments to asmooth cooktop stove.

The present invention is also applicable, not just to stoves and relatedappliances, but to any other surface that one may need to be warned thatit is hot. There are numerous devices whose surfaces become hot andremain hot even after the device has been shut off either electricallyor otherwise. For example, a radiator cap becomes hot and remains hotfor a period when the vehicle and radiator are shut off. Also, any kindof piping that is a conduit for hot liquids is an example of a surfacethat one may need to be warned that it is hot. Other devices having hotsurfaces include hot surfaces on fireplace doors, flat irons, chafingdishes, coffee urns, heating pipes, home radiators, glue guns, ovendoors, portable heaters of the electric, oil and ceramic disc type,kerosene lamps, kerosene heaters, barbecue grills of the electric, gasor charcoal type, electric woks, electric skillets, deep fryers for homeor commercial use, heat lamps in self service cafeterias and salad bars,saunas including the metal box that generates and/or controls the heat,rotisseries, indoor grills whether gas or electric, tea kettles, woodburning stoves, hot electric rollers, hot wax holders used for beautytreatments, bonnet type hair dryers, synthetic braid trimmers, curlingirons, portable generators, steam cleaners especially such as in drycleaning facilities, hot water pipes that are exposed, hot waterheaters, furnaces, warming trays, light fixtures such as halogen lamps,popcorn makers (especially commercial ones), toasters, cappuccino andespresso makers, autoclaves used to sterilize instruments in a medicalsetting, movie projectors and other such hot surfaces. These and otherhot surfaces are exposed to children, maintenance works and ordinaryadult users.

Accordingly, there is needed a versatile, easily movable and mountable,removably attachable and detachable, and effective, convenient and easyto manufacture device for warning adults, workers and children instantlywhen any kind of surface, whether it be a stove of any kind or any othersurface, is too hot to touch. There is also a need for such a devicethat is both capable of installation on a previously purchased stove ofany known type, including cooktops, electric and gas stoves, and onethat is also capable of being manufactured as part of the stove by stovemanufacturers. The present invention addresses and satisfies all ofthese needs and provides other advantages.

There is also a need for an effective, convenient and easy to use, anddetachable heat alert safety device that is easily read and understoodfor warning adults and children when any surface is too hot to touch.Such a device should ideally be positionable at a variety of heights orpositions so that it can be custom tailored for children of differentheight.

Importantly, moreover, there is a need for a heat alert safety devicethat is versatile enough to be easily positioned on a hot surface andyet be able to be easily removed thereafter when it has served itspurpose—either with respect to that surface or it has served its purposewith respect to that particular individual or it has served its purposefor that individual for that particular moment—and then be repositionedelsewhere—either on another hot surface of another object or anothersurface of the same object or even another portion of the same surfaceof the same appliance. This is necessary because in order for the heatalert safety device of the present invention to be effective it has tobe visible (or at least discernable) and in addition it should bediscernable and effective for children, and since children of differentages are of different heights it is advantageous to be able to attachthe device to. It is also necessary because a particular individual maydecide to relocate the heat alert safety device when a differentappliance is used or when a different portion of a kitchen counter isused, or when any other object with a hot surface is activated. Itshould be noted that by “activated” is included situations when anobject is “hot” a certain amount of time after the source of the heatwas “on” and it is of course not intended that the device of the presentinvention is limited to situations when electricity is “on” for anappliance or other object.

In light of the above discussion there is a need for a device which (i)is suitable for temperatures at least up to a high temperature of a gasoven (500° F.) (ii) is capable of conveying information at a grazingangle of sight, relative to the surface the device is mounted on (iii)may be detachably mounted on an existing surface. It is believed that noheretofore known product simultaneously meets these requirements. Itwould also be advantageous if the device were simple and rugged andcould withstand chance mishandling or rough treatment.

SUMMARY OF THE INVENTION

In the present invention chemical compositions that change color andremain at that color when they reach or exceed a certain temperature(referred to generally herein as “thermochromic compositions”), such ascholesteric liquid crystals or various types of liquid crystal polymersdesigned to turn color when they reach a certain temperature, and thatare shaped in the outline of the word “HOT” are embedded in a deviceattachable to or forming a part of any hot surface such as the topsurface of the heating element of stoves so that they change color andinstantly alert anyone, including a child, that the heating element ofthe stove is too hot to touch even when the stove or other device is“off”.

The present invention is a lightweight convex button type temperaturesurface warning device, or “hot button”. The device preferably fits inthe palm of the human hand and resembles a campaign button's outershape. The device is distinguishable over earlier art in that a warningsignal represented by a thermochromic material is visible over asubstantially increased arc, at least up to grazing angles with a notsurface, whereas at such angles existing flat indicators would beuseless. A “grazing angle” is any small angle approximately less than10°, and down to and including 0°. In some embodiments and applications,a warning signal may be visible below a grazing angle, i.e., from anangle of sight below the hot surface. In one embodiment a thermochromiccomposition is enclosed in an optically clear, physically rugged andconvex button or lens, typically manufactured of tempered glass. Inanother embodiment, the thermochromic composition is embedded in aconvex surface of such a button, which in this embodiment may be opaque.The thermochromic composition is however preferably embedded in a backside of the button which is manufactured out of a moderately heatconductive material like glass, to minimize a thermal lag between theprotected surface and the indication, whereas a button manufactured outof a good thermal conductor such as aluminum will functionsatisfactorily with the thermochromic composition embedded in the frontsurface. The rear surface of the button may be either flat or concave.

In any case the device is entirely constructed out of material able towithstand repeated cycling to a temperature of approximately 500 degreesFahrenheit or more, and able to withstand rough treatment. Thethermochromic material is shaped in a predetermined symbol or shape,such as the English letters “HOT” or such letters in another language,or in the background of such a symbol, communicating to a viewer that asurface is dangerously hot. The symbol may also take the form of aexclamation point, an international “no” symbol superimposed a stickdiagram of a figure touching a surface, a stylized human face showingshock or pain, a representation of flames, or any other recognizablewarning symbol. Preferably, although not necessarily, the symbol or itsbackground should lie in the color range red-orange-yellow, commonlyrecognized colors of both high temperature objects and of requiredcaution.

In a further embodiment of such invention, the warning symbol isrepeated or a pattern of thermochromic material is extended over alarger portion over a first or rear side of a convex button or lens sothat a warning signal is yet more viewable over a wider range of anglesfrom a second or front side of the button. The words “HOT! HOT! HOT! mayfor example be repeated in a horizontal strip running across or behind aconvex face so that at least one complete word is visible from a largerrange of horizontal angles. Alternatively an abstract pattern such asalternating wavy lines or a field of exclamation points, normallyinvisible and becoming red and black at a predetermined temperature, canbe continued across a front or back surface of the button, so thatportion of the pattern visible to a viewer on the front side of thebutton will suffice to convey the warning.

As discussed in the background section, visibility of a flat warningsignal is usually unacceptable greater than 70° to either side of anormal (perpendicular line) of the protected surface, and rapidlybecomes worse as the viewing angle approaches 90°. The “viewing angle”or angle formed with the normal to the surface is also referred to asthe angle of incidence, or in particular the angle of incidence of theline of sight. In contrast to a flat panel display, the device of thepresent invention allows a warning to be communicated to a user atviewing angles up to 90° from the vertical, or grazing the surface. Thewarning signal in some applications will even be visible from slightlybeneath the surface—an angle of incidence greater than 90°—provided aline of sight exists from the observer to a projecting portion of adisplay face of the device. The wide range of visibility is achieved bya use of clear material as a convex container for a thermochromiccomposition, and by an optional tiltable mounting enabling orientationof an axis of maximum visibility to be repositioned. Alternatively theeffect is achieved by using a cap of heat conducting and possible opaquematerial, such as aluminum, with a thermochromic material on or in aconvex front surface of the cap. This arrangement is also optionallycombined with a tiltable mounting.

The utility of this invention where a person may be tempted to reacharound a corner to grasp a handle on a hot surface or when a small handis attached to a child tempted to reach on top of a stove, will bereadily appreciated.

In optional embodiments of such invention a preferred range or solidcone of viewing angles is selectable by pivoting a button elementmounted on an end of a stalk. This arrangement is also called a“mushroom” arrangement. The stalk in this case is long enough to permita pivoting through a predetermined range of angles of the head or buttonwithout interfering with the protected surface. In cases where the pivotis not used the stalk may be shorter, any length down to a minimumthickness necessary for mounting on a surface.

The hot-button is temporarily affixed to ferrous (magnetic) surfaces bymeans of high-temperature resistant ceramic magnets, which are usable upto approximately 800° F. For yet higher temperatures, such as a side ofcoal-fired barbeque grills, a high temperature cement is used topermanently attach the button to the surface. Some embodiments mayinclude a metal backing welded to a screw thread or other attachmentpost, which may be passed through a hole in a metal or glass surface andsecured, for example, with a lock-washer and nut.

The unique features of the present invention include the large range ofviewing angles achieved by a combination of optical and geometricalmeans, combined with a temperature service range extending at least to500° F., rendering the device suitable for ovens and other cookingappliances, and visible at a grazing angle to the surface.

For completeness, various other embodiments which were disclosed in myprior application, of which this application in a continuation-in-part,will now be summarized.

In another embodiment described and claimed in my previous patent, U.S.Pat. No. 6,104,007, for use on electric stoves, the device is animproved electric coil whose central area contains the liquid crystals.In a second embodiment for use on smooth cooktop stoves, wall ovens andtoaster ovens, the thermochromic display is embedded in the glass areasthat form the heating elements of the smooth cooktop stove. As analternative to the second embodiment, for smooth cooktop stoves, thethermochromic display is in the shape of a ring surrounding the heatingelement (and visible when pots are placed on the heating element) whichring may have an interrupted area in the outline of the letters “HOT”).In a third embodiment for gas stoves also described and claimed in U.S.Pat. No. 6,104,007, the thermochromics are embedded in a recessed diskmounted on top of the central element of the gas stove's burner. In eachembodiment, the thermochromics stay red as long as the temperature theysense exceeds a certain degree Fahrenheit, such as 115 degreesFahrenheit, which has been found to be too hot to touch. In a fourthembodiment for use on wall ovens and toaster ovens, the thermochromicdisplay is embedded in the glass areas that form the heating elements ofthe smooth cooktop stove.

In one embodiment described in detail herein, in order too achieveremovable attachability and placement, the heat alert safety device ismade of two part, a half-dollar disk made of Pyrex and containing thethermochromic composition and an attachment and heat conducting elementin a disk in the shape of a dime on the back of the half-dollar shapeddisk.

Objects and Advantages

The following important objects and advantages of the present inventionare:

-   -   (a) to provide a device that instantly warns anyone including a        child that the surface of a stove, hot plate, the window of a        toaster oven, or other hot surface is too hot to touch,    -   (b) to provide a versatile heat warning device that can be used        for smooth cooktop stoves having any kind of surface including        glass or metal and using any kind of technology including        electric heating, electric induction and halogen light heating,        or can be used for electric stoves, or for gas stoves, for wall        ovens, for toaster ovens, for hot plates or for warming trays,    -   (c) to provide a device visible to the extent of providing a        warning through an arc of at least 180 degrees about the        vertical to a protected surface,    -   (d) to provide a heat warning device that is easy to manufacture        and that can be either installed onto the stove (or other        appliance's) heating element or can be manufactured as part of        the stove,    -   (e) to provide a heat warning device for stoves that can be        calibrated to produce a warning symbol only when a certain        temperature, such as 115 degrees Fahrenheit, is reached and that        can remain in signaling mode as long as such temperature is        exceeded by the appliance surface,    -   (f) to provide a heat warning device as above that makes use of        thermochromics that change color when a certain temperature is        reached, such as cholesteric liquid crystals or cadmium sulfide        semiconductors designed to change color when a certain        temperature is reached,    -   (g) to provide a heat warning device that is removably        attachable to a wide variety of hot surfaces in a very simple        manner,    -   (h) to provide a heat warning device that can is readable by        children and whose placement can be adjusted when the child        grows taller,    -   (i) to provide such a heat warning device that can be angled for        easier reading on surfaces in out-of-the-way locations such as        pipes,    -   (j) to provide such a heat warning device that contains a magnet        or an electrically conductive plastic that makes the device        removably attachable to any hot metal, glass or other suitable        surface and capable of receiving heat transmitted from the hot        surface and transferring it to the thermochromic composition        that changes color when a certain temperature is reached    -   (k) to provide a heat alert safety device that is readily        attachable to and detachable from hot surfaces on fireplace        doors, radiator caps, irons, chafing dishes, coffee urns,        heating pipes, home radiators, glue guns, oven doors, portable        heaters of electric, oil and ceramic disc, kerosene lamps,        kerosene heaters, barbecue grills of electric, gas or coal,        electric woks, electric skillets, deep fryers for home or        commercial use, heat lamps in self service cafeterias and salad        bars, saunas including the metal box that generates and/or        controls the heat, rotisseries, indoor grills whether gas or        electric, tea kettles, wood burning stoves, hot electric        rollers, hot wax holders used for beauty treatments, bonnet type        hair dryers, curling irons, portable generators, steam cleaners        especially such as in dry cleaning facilities, hot water pipes        that are exposed, hot water heaters, furnaces, warming trays,        light fixtures such as halogen lamps, popcorn makers (especially        commercial ones), toasters, cappuccino and espresso makers,        autoclaves used to sterilize instruments in a medical setting,        movie projectors and other such hot surfaces and (l) to provide        such a heat warning device wherein the thermochromic composition        turns invisible at the trigerring temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a gas stove having the device of thepresent invention on each burner.

FIG. 2 is an enlarged fragmentary plan view of a heating element of agas stove having the device of the present invention.

FIG. 3 is an enlarged fragmentary cross-sectional view taken along line3-3 of FIG. 2.

FIG. 4 is the prior art smooth cook top stove showing light indicators.

FIG. 5 is a top plan view of the device of the present invention used onan electric stove.

FIG. 6 is an enlarged fragmentary plan view of one heating element of anelectric stove having the device of the present invention.

FIG. 7 is an enlarged fragmentary cross-sectional view taken along line7-7 of FIG. 6.

FIG. 8 is a top plan view of the device of the present invention on thesmooth surface of a cook top stove.

FIG. 9 is an enlarged fragmentary plan view of one heating element of asmooth cook top stove having the device of the present invention.

FIG. 9A is an enlarged fragmentary plan view of one heating element of asmooth cook top stove and having the device of the present invention inthe shape of a ring surrounding the heating element.

FIG. 10 is a enlarged fragmentary cross-sectional view taken along line10-10 of FIG. 9.

FIG. 10A is a enlarged fragmentary cross-sectional view taken along line10A-10A of FIG. 9A.

FIG. 11 is a front elevational view of a wall stove having the device ofthe present invention.

FIG. 12 is an enlarged fragmentary front elevational view of one heatingelement of a smooth cook top stove having the device of the presentinvention.

FIG. 13 is a enlarged fragmentary cross-sectional view taken along line13-13 of FIG. 12.

FIG. 14 is a front elevational view of a wall oven having the device ofthe present invention.

FIG. 15A is a side view of an alternative embodiment of the device ofthe present invention.

FIG. 15B is a front view of an alternative embodiment of the device ofthe present invention.

FIG. 15C is a side view of the device of FIG. 15A except showing analternative embodiment of the device of the present invention.

FIG. 16A is a side view of an alternative embodiment of the device ofthe present invention.

FIG. 16B is a front view of an alternative embodiment of the device ofthe present invention.

FIG. 17A is a side view of an alternative embodiment of the device ofthe present invention.

FIG. 17B is a front view of an alternative embodiment of the device ofthe present invention.

FIG. 18A is a side view of an alternative embodiment of the device ofthe present invention for attaching to rounded hot surfaces.

FIG. 18B is a side view of an additional alternative embodiment of thedevice of the present invention for attaching to rounded hot surfaces.

FIG. 19 is an alternative embodiment of the device of FIG. 16A that canbe positioned at different angles.

FIG. 20A is an alternative embodiment of the device of FIG. 15Aincluding a straight face.

FIG. 20B is an alternative embodiment of the device of FIG. 16Aincluding a straight face.

FIG. 21 is partly a cross-section and partly a side view of anembodiment employing an alternate means of attachment of the presentinvention to a flat surface.

FIG. 22A is a first cross-sectional view showing an embodiment employinganother alternate means of attachment to a flat surface.

FIG. 22B is a second cross-sectional view of the embodiment of FIG. 22A,further showing the means of attachment to a flat surface.

FIG. 23A is a diagram showing a geometry of the viewing angles for anobject mounted on a flat surface.

FIG. 23B is a diagram showing a geometry of an increased viewing anglefor an object mounted on a flat surface.

FIG. 23C is a diagram showing a modification of the geometry of FIG. 23Afor the viewing angles of an object mounted on a flat surface.

FIG. 24 is a schematic view showing a line-of-sight in a first geometryof the present invention.

FIG. 25 is a schematic view showing a line-of-sight in a second geometryof the present invention.

FIG. 26 is a schematic view showing a line-of-sight in a third geometryof the present invention and

FIGS. 27A, 27B, 27C and 27D are side views of four differently-shapedalternative embodiments of the device of the present invention having aconvex face.

FIGS. 27E and 27F are side and front views respectively of a furtheralternative embodiment of the device of the present invention having aconvex face

DETAILED DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention disclosed in my prior applicationof which this application forms a continuation-in-part and in my priorbelow-identified U.S. Patent will first be recited for completeness.Thereafter the specific embodiment which is the material of this patentwill be described.

One of the embodiments of the present invention, as described andclaimed in my previous patent, U.S. Pat. No. 6,104,007, is for stovesthat employ gas heat, as seen in FIGS. 1-3. In this embodiment, the topof the stove 100 typically has four heating elements 7, that are calledburners and that are covered by metal grates 9, that are open in themiddle. Each burner or heating element is situated in a recessed area 8and is surrounded by the metal grate. As best seen in FIG. 2, there is acentral metal element 10 in which a series of gas outlet holes on theside 10 a of the central metal element permit gas to flow through andignite. As seen in FIGS. 1-3, the central metal element 10 has a disk 12on a top surface 12 a of the central metal element 10 and this disk 12contains thermochromic materials 14 in the form of the letters “HOT”that change color when they reach a certain temperature. Alternatively,the central metal element 10 itself can have embedded therein on its topsurface the thermochromic material 14 in the shape of the letters “HOT”using known methods.

The temperature of the grates upon which pots and pans rest duringcooking may be roughly equal or greater than the temperature of thecentral metal element 10. Accordingly, whenever the letters “HOT” becomered both the grates and the central metal element may be too hot totouch. There may be some discrepancy between period of time needed forthe grates to cool enough to be safely touched, and the period of timethe central metal element 10 requires to cool enough to be safelytouched. As an option to take into account any discrepancy between thetime at which the central element 10 becomes cool and the time at whichthe metal grates become cool the temperature at which the thermochromiccompositions 14 (such as cholesteric liquid crystals or various types ofliquid crystal polymers designed to turn red at a specific temperature)turn red, the transition temperature, can be adjusted to a lowertemperature, so that if either the grates or the central metal element10 is too hot the thermochromic material 14 will remain red.

FIGS. 5-7 depict an embodiment of the present invention described andclaimed in my previous patent, U.S. Pat. No. 6,104,007, for the topsurface of electric stoves. Electric stoves typically have four heatingelements on the top of the stove made of electric coils 20 wound in aserpentine configuration and sitting on a metal rest 21. Normally,electric coils 20 have a recessed disk 22 in a central area of each coil20 that is connected to and held up by the metal rest 21. FIG. 5 showstop plan view and FIG. 6 shows an enlarged fragmentary plan view ofelectric coil 20 of the present invention having central disk 22containing thermochromic composition 24 (which may be cholesteric liquidcrystals or various types of thermochromic polymers designed to turncolor at a specific temperature) that are in the shape of the letters“HOT” embedded on the top surface 22 a thereof. The thermochromicmaterial 24 become red whenever the temperature of central disk 22exceeds 115 degrees Fahrenheit and remains red unless the temperaturefalls below this value. This heating element may be made by embeddingthe thermochromic material 24 on the top surface 22 a of the centraldisk 22 using methods well known in the art. Alternatively, existingelectric stove heating elements can be modified by fitting thereon adisk containing on its top surface thermochromic material 24 embeddedtherein.

The central disk 22 containing thermochromic material 24 in the shape ofthe letters “HOT” embedded on the top surface 22 a is recessed roughly aquarter of an inch below the surface of the electric coil 20 so thatwhen pans and pots are placed on the electric coils they do not scratchthe central disk 22.

As an option, since there may be some discrepancy between thetemperature of the electric coil 20 and that of the central disk 22, thetransition temperature at which the thermochromic material 24 turn red,can be set to be the lower than the temperature required to be safe totouch, so that when the thermochromic element reverts to its lowtemperature color the user may be sure the coils also are safe to touch.This way, someone is warned against touching either the central element22 or the actual coil 20.

FIGS. 8-10 depict an embodiment of the present invention for use withsmooth cooktop stoves, sometimes called “smoothtops” or “cooktops”. Forcook top stoves, the prior art is shown in FIG. 4. As seen in FIGS.8-10, smooth cooktop stoves have heating elements that consistessentially of an area of glass surface 30 that is smooth on top andwhose underside is made dark enough to absorb light. Such absorptiongenerates heat in the smooth area of glass 30. Underneath each area 30,usually circular, is a strong light source 36, such as a halogen lights.The light source 36, as seen in FIG. 10, projects the light upward tothe surface area of the smoothtop's heating element—the glass area 30 onthe top surface of the stove. Since each glass area is coated on itsbottom with a dark coating, when the light strikes the bottom of theglass areas the heat from the strong light is absorbed by the darkenedportion of the smooth area of glass 30. These glass surfaces 30 form theheating elements of the stove. Cooking utensils are simply placed overthe area (which may be square, round, etc.) of the heating element onthe glass surface. Some smooth cooktop stoves employ “radiant” heatsources for the glass areas instead of halogen light sources 36 but theeffect is the same. In addition, some smooth cooktop stoves have halogenlamps (under each area 30 as before) but they emit infrared waves thatprovide light and heat.

The heat alert device of the present invention when used for the smoothsurface of cooktop stoves of either type would comprise thermochromiccomposition 32 embedded in the top surface of each glass area 30, whichis the heating element on the smooth cooktop stove using known methods.For example, the thermochromic composition 32 may be made in the exactshape of the letters “HOT” by spraying the composition of thermochromicmaterial 32 over each glass area 30 after covering the glass area 30with a cardboard stencil or other cut-out in the outline or shape of theletters “HOT”. As before, the liquid crystal or thermochromiccomposition is designed to turn red and remain red whenever thetemperature of the smooth area of glass exceeds a specified temperature,such as 115 degrees Fahrenheit.

As an alternative embodiment for smooth cooktop stoves, with such stovesusing any technology including electric heating, electric induction andhalogen light heating, the thermochromic display is in the shape of aring surrounding the heating element (and visible when pots are placedon the heating element) which ring may have an interrupted area in theoutline of the letters “HOT”, as seen in FIGS. 9A and 10A. Thisaddresses and solves the problem that people often leave pots or kettleson the stove perpetually and that with smooth cooktop stoves the resultof doing so is that the heating element is no never visible (since thepot or kettle may be as large or large than the heating element). Insuch situations, no matter how mature, cautious and alert you are, youcannot readily ascertain that the heating element (and the kettle or potabove it) is too hot to touch. By seeing the ring of the presentinvention (with or without the letters “HOT” filling an interruptedportion thereof) lit up as red, you immediately know that the area ofthe heating element is too hot to touch. In this embodiment, thethermochromic composition 32 is embedded on the stove surface in theoutline of a ring (and in the letters “HOT”) in a location ofsurrounding the heating element, i.e. surrounding the top surface of thesmooth glass or metal areas 30 on the stove surface 31.

Although FIGS. 8-10 (including FIGS. 9A, 10A) have been described interms of smoothtops with heating elements made of smooth glass surfaces,other variations of smooth top stoves exist—in particular smooth metaltops called electric cooktops. The difference is that a light source 36would not be used under the surface to generate heat—instead the metalgets hot by being connected to a heat source that may be electric (notshown). In addition, some smooth cooktops use a “ribbon heating element”instead of halogen light sources where the smooth glass surface isheated by a coiled electric circuit called a “ribbon element” directlyand immediately underneath the glass instead of by a halogen lightsource. The device of the present invention works the same way for metalcooktops, glass cooktops and for those that rely on halogen light sourceas the heat or those that use ribbon heating elements. FIGS. 8-9 whichdepicts the present invention for use with glass cooktops also depictsthe present invention as applied to smooth metal cooktop stoves and asapplied to ribbon heating elements. FIG. 10, which describes the presentinvention for use with glass cooktops that employ halogen light sources,the top part of FIG. 10 also depicts a cross section of thethermochromic composition for smoothtops—for metal cooktops and glasscooktops using ribbon heating elements the halogen light source 36 wouldnot be present but everything else would be the same. For all of thesmooth cooktops, the thermochromic composition 32 would still beembedded in the top surface of the smooth metal areas 30 on the stovesurface in the shape of the letters “HOT”.

Other variations of smooth cooktops also exist and the thermochromiccomposition in the shape of the letters “HOT” can also be embedded intheir surfaces. For example, some smooth cooktops have a raised solidelement having a smooth top and made of metal having a recessed centralarea. The thermochromic composition would be embedded in this recessedcentral area as before in the shape of the letters “HOT”.

FIGS. 11-13 depict a wall oven whose window surface 40 has embeddedthereon the thermochromic composition 46 of the present invention in theshape of the letters “HOT”. As before, the thermochromic composition 46is designed to turn red and remain red whenever the temperature of thesmooth area of glass exceeds a specified temperature, such as 115degrees Fahrenheit. The purpose is to warn children or adults not totouch the surface of the window 40 that gets very hot when the oven ison. There is not present a convenient and effective warning method inuse for the vertical surfaces of oven windows. This is particularlyimportant since when the oven is turned off, the window 40 remains hoteven though it appears that everything is off.

Toaster ovens also have a window surface 40 which would have embeddedthereon the thermochromic composition 46 of the present invention in theshape of the letters “HOT”. As before, the thermochromic composition 46is designed to turn red and remain red whenever the temperature of thesmooth area of glass exceeds a specified temperature, such as 115degrees Fahrenheit.

Hot plates can be thought of as small mobile electric stoves having oneheating element. Warming trays can be thought of as small mobile smoothcooktop ovens having one smooth surface as a heating element. In both ofthese cases, the hot plate and the warming tray, the present inventionwould be applied to the heating element and function the same way asdescribed with respect to their larger and more permanentcounterparts—the electric stove and the cooktop stove.

It should be noted in general that the present invention makes use ofany thermochromic composition that changes color and remains at thatcolor when a specified temperature is reached or exceeded—it need notnecessarily be cholesteric, although it has been found that cholestericliquid crystal material does this effectively. It is also within thescope of the present invention to make use of a thermochromiccomposition that changed color when it reached a specified temperatureor temperature range but changed to a third color at a higher thresholdtemperature, so long as the third color is significantly different fromthe first color—although this would certainly not be the ideal kind ofthermochromic composition. The ideal composition turns red at aspecified temperature and remains red above that temperature.

The ideal heat warning symbol is a color known to represent warning,such red or orange, although as indicated any color is contemplated bythe present invention.

It should be understood clearly that the thermochromic composition ofthe present invention reveals a predetermined symbol whenever and solong as the temperature of the surface that the composition is onexceeds a predetermined temperature. This can be arranged in more thanone way. For example, this can happen as a result of the thermochromiccomposition turning color and being shaped in the shape of the heatwarning symbol (or the background of such symbol). It can also happen asa result of the thermochromic composition covering the heat warningsymbol and then becoming invisible at the triggering temperature.

In either case, the thermochromic composition, when the triggeringtemperature is reached, simply turns into a color that makes the symbolreadily visible. For example, the thermochromic composition can turn redat the triggering temperature and be shaped in the form of the symbol orshaped in the background of the symbol. The second way is that thethermochromic composition, until the triggering temperature occurs,blocks the visibility of a red heat warning symbol underneath it. Whenthe triggering temperature arrives, the thermochromic compositionbecomes invisible and reveals the underlying red symbol.

In either case, it is preferable that the entire heat warning symbol andthe thermochromic composition be substantially invisible against abackground color of the surface prior to the triggering temperaturebeing exceeded. This is so that the presence of the heat warning devicebe unknown prior to the triggering temperature being exceeded. This hastwo advantages: (i) the warning is more dramatic when it arrives and(ii) the presence of the warning does not clutter or mar the appearanceof the surface of the stove or other appliance.

In the case where the thermochromic composition covers a previouslywritten or formed heat warning symbol, preferably, the heat warningsymbol was formed or written underneath the thermochromic composition bywhatever well known processes employ the least expensive means, such asprinting, writing, stamping, scratching, etc. Accordingly, although thedrawing figures of the present invention (especially FIGS. 1-26) mayseem to be directed to the case in which the thermochromic compositionis itself in the shape of the letters “H,O,T” or other heat warningsymbol, it should be understood that the drawings could just as well bedepicting the case in which the thermochromic composition has turnedinvisible (since the temperature has exceeded the predeterminedtemperature) and has revealed beneath said composition the heat warningsymbol such as the letters “HOT” printed or otherwise fixed onto sometangible medium of expression such as paper or any other object.

The point of one feature of the present invention is to use thethermochromic composition to create a color contrast between a colorsuch as red or some other color in order to depict the letters “HOT” inred or that color whether by virtue of the thermochromic compositionitself being the letters “HOT” or whether the thermochromic compositionsurrounds the letters and in effect constitutes everything else exceptthe letters “HOT” or whether the thermochromic composition covers apreviously inscribed symbol and becomes invisible to reveal such symbolat the triggering temperature.

In some embodiments, when the temperature of the surface does not exceedthe predetermined temperature the thermochromic composition is notreadily visible against a background color of the hot surface. Althoughsince the device has some bulk the device is not invisible, the deviceblends into the background color of the hot surface and is not soreadily visible. If the thermochromic composition turns invisible whenthe predetermined triggering temperature is reached and is opaqueotherwise, the convex face of the device of the present invention (whichfrom most angles is the only part or almost the only part of the devicethat a viewer sees) is the same or almost the same color as the color ofthe hot surface to which the device is attached. This further dramatizesthe appearance of the heat warning symbol when the temperature doesexceed the predetermined temperature.

With use of the present invention, when an individual enters the kitchenwith the cook top stove in it he or she can instantly recognize if anyof the heating elements are too hot. This is in contrast to the priorart for which the person would have to first figure out which heatingelement corresponds to which light indicator.

The present invention contemplates that other letters and other lettershapes besides that of “HOT” could be used as a warning although it isbelieved that the simple arrangement of the letters “HOT” in a boldsimple typeset provide the best warning. Furthermore, the presentinvention also contemplates that the thermochromic composition in theoutline of the letters “HOT” can be embedded in a surface of a stove,toaster oven or other appliance where the surface is vertical andperpendicular to the floor, not only horizontal. In addition, while thedrawings depict the thermochromic composition embedded on the surface ofthe stove in a particular configuration and depth, it is contemplated bythe present invention that the depth and configuration of thethermochromic composition can vary and still be within the scope of thisinvention.

It is also contemplated by the present invention that glass diskscontaining thermochromic compositions in the shape of the letters “HOT”can be made so as to be purchased separately by the consumer as a glassdisk having embedded therein the thermochromic composition to be affixedto a glass surface area of a cooktop stove, a wall oven or a toasteroven.

It is also contemplated by the present invention with respect to allembodiments that in addition to the thermochromic composition being inan outline of the letters “HOT”, the thermochromic composition couldinstead be in the background of such an outline. By this is meant thatthe thermochromic composition would form the entire area except anoutline of the letters “HOT”. The point of one feature of the presentinvention is to use the thermochromic composition to create a colorcontrast between red and some other color in order to depict the letters“HOT” in red whether by virtue of the thermochromic composition itselfbeing the letters “HOT” or whether the thermochromic compositionsurrounds the letters and in effect constitutes everything else exceptthe letters “HOT”. Furthermore, it should be noted that in this patentapplication, the term “red” refers to all possible variations and shadesof the color red as well as to all possible variations of the colorsorange and yellow. Red and orange and yellow are the colors associatedwith heat. Furthermore, if the hot surface (as opposed to the area ofthe thermochromic composition) itself is or becomes red when hot, thenthe thermochromic composition 230 would have to be orange and viceversa.

Hot Button Embodiment

The “hot-button” or “mushroom” embodiment of the invention is nowdiscussed. This embodiment provides a detachable device which may beapplied to existing surfaces, and is designed to be visible through awide and optionally selectable angle of view.

In order to be effective, a warning must be visible. Furthermore, inorder to be processed quickly by the human brain, a warning must beclearly visible, a condition which for the purposes of this patent shallbe deemed “substantially visible”, which condition will be preciselydefined.

As a preliminary, FIGS. 23A, 23B, 23C illustrate geometrical conceptsmentioned in the specification. A smooth surface S has an abstractnormal or perpendicular line N, as shown in FIG. 22A. In general acircularly symmetric warning device affixed to surface S (not shown)will be usefully visible through a cone or solid angle C defined by anangle α. When an object is said to be “substantially visible through anangle α with the normal”, it will mean in terms of an angle α sodefined. An object or symbol will further said to be “substantiallyvisible through an angle α with the normal” when it is visible in atleast one direction of tilt from the normal through this angle, that is,in at least one half plane. The cone of visibility need not in fact be acircular cone, although it may be. If the maximum angle of visibility isnot constant with rotation about a normal axis to the surface, it willbe taken as the largest such value.

The precise meaning of “substantially visible” will now be defined. Toallow enough reaction time to avoid touching a hot surface an individualmust be able to readily perceive a warning from at just outside of arm'slength: the minimum warning distance is taken as three feet. To beusefully visible to a person of near normal visual acuity at a distanceof three feet a symbol and its background must subtend a minimum viewingarea in the line-of-sight: this minimum viewing area is taken as ¼″ by¼″ (at least ¼″ in each dimension). By “subtend” it is meant that theviewing area of the object or symbol—and immediate background—isprojected on a surface perpendicular to the line-of-sight. This isgeometrically illustrated by the relation of a length of line segment Pin FIG. 26 to the visible dimension of face 744 of cap 740.

Furthermore, “substantially visible” limits the angle of incidence ofthe line of sight with the surface on which a symbol is represented. The“angle of incidence of the line of sight with the surface” is just thesame angle α as defined in FIG. 23A. The reason for this limitation isthat the “specular” or mirror reflectance of almost all materialsincreases with the angle of incidence of light; that is, materials actmore like mirrors at large angles of sight to the vertical (small anglesof sight with respect to the surface). This increasing mirrorreflectance tends to swamp the contrast of a displayed symbol,especially one lit by ambient lighting, as the viewing angle increases.

For the purposes of this invention it is judged that a portion of asurface displaying a symbol is not usefully visible if the viewing angleor line-of-sight exceeds 70° from the vertical. That is, to be“substantially visible” from a given angle, portions of a surfacedisplaying a symbol or at least contributing to the required ¼″ by ¼″subtended area, must have a normal at no more than 70° to the line ofsight.

By way of illustration, a 1″ by 1″ flat display, viewed at an angle of60° to the normal, would subtend an apparent area of 1″ by ½″. In thatexample, as best appreciated from looking at FIG. 26, in one dimensionthe range of vision is decreased by 50% because the cosine of 60° is ½.The other dimension is unaffected so the area is 1″ by ½″. Since 1″ by½″ exceeds ¼″ by ¼″, and since 60° is less than 70°, this display isjudged to meet both requirements, and be “substantially visible” fromthis viewing angle, or line-of-sight.

If the same display is viewed from an angle 80° to the normal, theapparent area subtended is now approximately 1″ by 0.19″. Since 0.19 isless than 0.25, or ¼, the display fails to be substantially visible fromthis angle on this criterion, even though the total area subtended isgreater than ¼″ times ¼″, or approximately 0.06 square inch.Furthermore, even if the overall display sized were increased to 2″ by2″, so that the apparent viewed area were 2″ by 0.38″, this displaywould be deemed not substantially visible at this angle, since 80° isgreater than 70°. These concepts will subsequently be developed furtherin relation to FIGS. 24, 25 and 26.

FIGS. 15 through 20 depict several alternative shapes for a versatileheat alert safety device 200 of the present invention. The versatileheat alert safety device of the present invention is designed to addressmany of the needs outlined, including the need for a device that can beattached to a hot surface and later removed and re-attached either to adifferent hot surface or a different part of the same hot surface, onethat is rugged, suitable for temperatures of 500° F. or greater, and isviewable from a wide range of angles. The hot surfaces are typicallymetal or glass but can be of other suitable materials.

In each of the shapes shown in FIGS. 15-20, the device is essentiallycomprised of two parts, an attachment part and a container part havingthe thermochromic composition, each of which is adjacent to the other.In some cases, the parts are attached like a dime affixed adhesively tothe back of a half-dollar (of U.S. currency). It should be noted thatfor the embodiments depicted in FIGS. 15-20 the overall device of thepresent invention has been assigned the reference numeral “200”.

As seen in FIGS. 15A and 15B, the first part of device 200 is theattachment element 220 that is a thin disk that may be round or square.Attachment element 220, which is attached to the metal or glass surface(not shown), conducts heat. Attachment element 220 may be either amagnet or else a thermally conductive but non-magnetic material. Thismay be a traditional material such as aluminum, or a more modernmaterial such as an electrically conductive plastic. Electricallyconductive plastics are also good thermal conductors. Such non-magneticattachment elements would also either have adhering characteristics sothat device 200 that are sufficiently strong to adhere the device 200 tothe hot surface but sufficiently weak so that the device 200 can beremoved from and hence be removably attached to the hot surface.Alternatively, the heat conducting plastic would have a layer of weaklyadhering plastic of any kind at a rear surface that comes into contactwith the hot metal, glass or other surface. Plastics made of polymersthat conduct electricity and transmit heat are known to organicchemists. This attachment element 220 makes the device 200 removablyattachable to virtually any hot surface.

The second part of device 200 is composed of the thermochromiccomposition 230 itself and a container 240 for containing these crystals230. In all embodiments of the present invention, the container elementof the device has a face that is convex that overlies the thermochromiccomposition 230 and that is transparent in at least a portion of thecontainer overlying the thermochromic composition 230. Technically, itis only the uppermost part of convex face 242 that need be convex.Hence, as seen in FIG. 15C, container 240 may also have a generallyplanar and substantially cylindrical sub-face 242 a below convex face242.

Ideally, curved face 242 of container 240 is convex and curved althoughtypically not rounded to the extent of being a hemisphere since if thecontainer 240 had too much of a height it would limit the range ofangles from which the letters “HOT” on curved face 242 can be seencompletely. Alternatively, container 240 may be extended to a completehemisphere or beyond, without sacrificing legibility, if the letters“HOT” or some other warning symbol is repeated in a pattern (not shown)on face 242, so that a recognizable portion of the pattern is visiblefrom a wide range of angles.

In all embodiments of the present invention except the “mushroom”embodiment (see e.g. FIGS. 16A, 16B) where the st, attachment element220 is preferably thin enough so that the shape of the container 240 andthe attachment element 220 together resembles an outer shape of acampaign button.

As an illustration of the geometry of a spherical cap or button, FIG.15A may further serve as a reference. The term “button” means somethingresembling, in shape and size, the visible side of a campaign button. Ifcontainer 240 is in a shape of a cap or section cut from a sphere (notshown) with diameter D, then the container will have a minor diameter dequal to the diameter of flat container attachment side 247. Thecontainer will also have a thickness h as seen from the side (FIG. 15A)equal to a perpendicular distance from side 247 to an extreme point 232of curved face 242. This thickness h is the minimum thickness which willallow proper visibility in a line of sight just grazing the protectedsurface.

The diameter of the hot button 200 of the present invention isrepresented by flat container attachment side 220 a. This diametershould be such that the thickness h as measured from perpendiculardistance from side 220 a to the farthest point 232 along curved face 242provides a side view of the hot button that allows someone from adistance of say 3 feet to see one or more letters of the message onthermochromic composition 232. The diameter should not be so great thatthe hot button 200 is too bulky or occupies too much of the surface areaof an object.

By way of particular example, suppose a person of normal visual acuitywill clearly see a letter of {fraction (5/16)} inch in width from adistance of 3 feet, which is at or beyond arm's length. Then the widthof {fraction (5/16)} for the hot button 200 can be achieved by havingthe hot button of various diameters depending upon the degree ofcurvature of the convex curved face 242. If container 240 of the hotbutton 200 was to be a perfect hemisphere, the diameter of container 240should be five-eighths of an inch in order to ensure that thickness h ininches of container 240 is {fraction (5/16)}. Actually, however,curvature of container 240 is flatter than a perfect hemisphere sincehot button 200 resembles the outer surface of a campaign button.

Accordingly, the width of {fraction (5/16)} for the hot button 200 willbe achieved approximately by cutting a cap with minor diameter d=2 andtwo-thirds inches from a sphere of radius R=3″. The cap will then beapproximately 2 and two-thirds inches in diameter and approximately{fraction (5/16)}″ in thickness. Other combinations of minor and majordiameters in the cap and sphere exist such that the cap would have athickness of approximately {fraction (5/16)}″ Since as seen in the FIG.15A at least one letter of even a single instance of “HOT” will bevisible from the side, this will suffice to convey the warning.

In these preceding examples, it will be understood that “cut” does notliterally mean that a piece must be cut from a complete sphere ofmaterial to manufacture a spherical cap.

Alternatively, and less ideally, straight face 242 a of container 340may be used, as seen in FIG. 20A. In this instance, warning symbols 342are optionally formed by thermochromic material embedded in a rim orouter circumference 344 of container 340. Container 240 is also somewhatdisk shaped in that it has a flat rear edge 247 (like the flat side of ahemisphere) that attaches to the flat container attachment side 220 b ofthe attachment element 220. Typically, although not necessarily,container 240 has a larger diameter than the diameter of the attachmentelement 220 because the diameter of container 240 should reflect thefact that it is desirable that the letters “HOT” on curved face 242 bewidely visible while the diameter of attachment element 220 need only belarge enough to yield a secure attachment of device 200 to the hotsurface.

Container 240 is made of a heat transmitting or conducting substancecapable of being transparent such as any of a variety of heat conductingglassware products sold under the name “Pyrex” or any heat transmittingplastic that is capable of being transparent. Curved face 242 ofcontainer 240 is transparent at least in the portion of curved face 242that covers the thermochromic composition 230. Accordingly, curved face242 displays the letters “HOT” when the surface to which the heattransmission element 220 is attached exceeds a specified temperature,for example a temperature above approximately 115 degrees Fahrenheit (°F).

The attachment element 220 of device 200 has a flat container attachmentside 220 b that is attached to the flat rear edge 247 of the container240 by a variety of means, such as by epoxy or by being welded if theheat attachment element is 220 is a magnet. The epoxy should of coursenot be so extensive that it impedes the heat transmission between thetwo parts of device 200.

As seen in FIGS. 16A and 16B, an alternative shape of device 200includes what is called a mushroom shaped container 340 composed of astem 345 and a convex face 346. Although stem 345 typically is of thesame material and forms an integral part of the rest of container 340and hence is usually described as forming of a portion of container 340with the non-stem portion of container 340 being called a container head340 a for convenience, for the purpose of illustrating the shape of theoverall device in the mushroom embodiment and comparing it to otherembodiments it is also convenient to describe stem 345 as separate fromcontainer 340 and as being mounted between container 340 and attachmentelement 320. Stem 345 is made of heat conducting material and designedto offset the container head 340 a of container 340 from attachmentelement 320 and hence also from the hot surface that the hot buttondevice is on. The overall device is substantially in the form of amushroom. Typically, and this is why it is referred to herein as“mushroom shaped”, stem 345 is narrower in diameter than convex face 346although it need not be, because convex face 346 has to be visiblewhereas stem 345 need only be wide enough for device 200 to be securefor attachment to the hot metal or glass surface by means of attachmentelement 320. Convex face 346 of container 340 houses the thermochromiccomposition 230 and is transparent at least in a portion of the face 346that covers the thermochromic composition 230. Alternatively, and lessideally, straight face 346 b of container 340 b may be used, as seen inFIG. 20B.

As in the shape shown in FIGS. 15A and 15B, container 340 in FIGS. 16Aand 16B is made of a heat conductive material. Unlike in FIGS. 15A and15B, in FIGS. 16A and 16B container 340 has a short cylindrical stem 345including a rear stem edge 345 a and has a convex face 346 that iscurved although typically not as much as a hemisphere. The thermochromiccomposition 230 is shaped in an outline of the letters “HOT” or in thebackground of such an outline. Thermochromic composition 230 is embeddedin the convex face 346 of the container 340 and is designed to turn redand remain red whenever the temperature of the hot surface exceeds aspecified temperature.

Device 200 shown in FIGS. 16A, 16B, as with device 200 shown in FIG. 15,includes attachment element 320 that is made of a heat conductivematerial and has a hot surface attachment side 320 a and a containerattachment side 320 b. Attachment element 320 is removable from andattachable to the metal or glass surface on the hot surface attachmentside 320 a. The rear stem edge 345 a on container 340 is flat andattaches to the flat edge of container attachment side 320 b of theattachment element 320.

As in FIGS. 15A and 15B, in FIGS. 16A and 16B, device 200 includescontainer 340 that is either a solid piece of heat transmitting plasticor any of a variety of transparent heat transmitting glassware such asthat sold under the name “Pyrex”. Likewise, convex face 346 displays theletters “HOT” when the surface to which the heat transmission element320 is attached is at a specified temperature, such as a temperatureabove approximately 115 degrees Fahrenheit. Rear stem edge 345 a ofcontainer 340 attaches to either a magnet 320, which since it is metaltransmits heat and is removably attachable to a hot metal or glasssurface, or else it attaches to a detachable adhering plastic that alsotransmits heat and whose adhesive strength is sufficiently weak that itis detachable yet sufficiently strong that it can adhere an object of adecent amount of weight to a smooth metal or glass (or other suitable)surface. An example of a heat transmitting plastic is polyacetylene. 3M,the well known company in Minnesota, manufactures and sells adhesivesthat are used for temporarily attaching objects that have significantweight to a surface.

As seen in FIG. 17, another alternative shape of device 200 is shown. Inthis embodiment there is an inner cylinder container 290, in the shapeof the hole of a doughnut, for housing the thermochromic composition230. Face 292 of inner cylinder container 290 ideally should be convexfor better viewing of the letters “HOT” (although face 292 could lessideally also be straight and not convex) and is transparent at least ina portion of face 292 covering the thermochromic composition 230. Innercylinder container 290 is made of a heat conductive material capable ofbeing transparent. As in FIGS. 15A, 15B, 16A, 16B, in FIG. 17 thethermochromic composition 230 is designed to turn red and remain redwhenever the temperature of the hot surface exceeds a specifiedtemperature. In this shape shown in FIG. 17, there is an outer cylinderattachment element 280 made of a heat conductive material and in theshape of a doughnut having a flat rear wall (not shown) for attaching tothe hot metal or glass surface. The inside wall 289 of the outercylinder attachment element 280 is attachable to the inner cylindercontainer 290 and the flat rear wall (not shown) of attachment element280 allows removable attachment of device 200 to a hot surface. Innercylinder container 290 is also flat on its inner cylinder container rearwall (not shown) and the inner cylinder container rear wall (not shown)is typically flush with the flat rear wall (not shown) of attachmentelement 280 in order to not impede the smooth attachment of device 200to a hot surface.

Each of the embodiments of device 200 depicted in FIGS. 15 through 20are versatile heat alert safety devices in that they are readilyattachable to and later detachable from any surface that may be hot evenafter the source of the heat has been shut off. Such surfaces caninclude metal or glass and may include the metal or glass wall of anyheat-producing appliance such as the wall of an electric stove, gasstove, smoothtop stove, oven, toaster or a metal crock pot. The hotsurfaces to which device 200 can be attached need not be restricted tometal or glass but can be other surfaces that can receive a magnet ortemporarily adhering adhesives.

Two or more sides or walls of an appliance can sometimes get hot and theone side might not be suitable to have a heat alert safety deviceattached to it even though the same heat alert safety device of thepresent invention is made specifically for the other side of the sameappliance. For example, a heat alert safety device of the presentinvention for the top of an electric stove is not suitable forattachment to a side wall of that stove. Device 200 as depicted in FIGS.15A, 15B, FIG. 16A, FIG. 16B, FIG. 17, FIG. 19 and FIG. 20 can beapplied to any wall of such an appliance since it can be applied to anyhot surface. This application is especially useful for kitchen workerssurrounded by multiple ovens and/or hot counters—they can place device200 on each such hot surface.

Other surfaces that get hot and to which device 200 can be usefullyapplied besides food related appliances include radiator caps locatedunder the hood of a car or other vehicle, piping through which hot steamflows, the surface of a curling iron, surfaces of a steam press and manyothers listed herein in the Objects and Advantages.

Accordingly, FIG. 18A shows a heat alert safety device 200 designedspecifically to be removably attachable to a rounded metal, glass orother hot surface, such as piping, that may be hot. In this embodiment,the heat alert safety device 200 may be of the same shape as the device200 of FIG. 16 (or alternatively FIG. 15) except with respect to theshape of attachment element 420 of the device 200 of FIG. 18. Since thedevice 200 shown in FIG. 18 needs to be attached to a rounded surfacesuch as a pipe, the container 440 for housing the thermochromiccomposition 230 has a short cylindrical stem 445 including a flat rearstem edge 445 a and container 440 has a convex face 446. Attachmentelement 420 has a concave hot surface attachment side 420 a and a flatcontainer attachment side 420, attachment element 420 is removable fromand attachable to the rounded hot surface on the hot surface attachmentside 420 a so as to allow the letters “HOT” to be visible. Flat rearstem edge 445 a attaches to the container attachment side 420 b ofattachment element 420. Alternatively and less ideally, as seen in FIG.18B, the concavity can also exist at the rear stem edge 445 a and at thecontainer attachment side 420 b of attachment element 420 (withidentical curvature).

Another feature of the present invention that enhances its versatilityis that device 200 can be positioned at a height suitable for a smallchild and can be repositioned later at a different height when the childis older and taller. In a family of many children of different ages andheights there would typically not be room on the walls of an appliancefor several different heat alert safety devices of the presentinvention. With the device 200 depicted in FIGS. 15-16, curved face 242of FIG. 15 and convex face 346 of FIG. 16 are convex or rounded so thatthe letters “HOT” thereon may be read from a variety of angles,depending upon the height (and angle of observation) of the observer.

Another way in which the device 200 of the present invention can be readfrom a variety of angles is that in one embodiment of device 200 itsangle of placement with respect to the observer is adjustable. Device200 can be positioned at different angles from the viewer to maximizethe potential for observers, particularly children, to be able to readthe letters “HOT”. This is especially valuable when the heat alertdevice 200 is affixed to difficult to access surfaces that may be hardto notice. It is critical that children actually be able to read theletters “HOT” for the device to be effective.

In the embodiment shown in FIG. 19, a device 200 has a convex cap 502which can be tiltably adjusted to present convex face 522 to variousviewing angles. The angle of the cap 502 may be chosen so that the childto be warned of the hot surface can most easily read the letters “HOT”on convex face 522. At the edge at which stem 545 meets convex face 522of container 540, well known rotation attachment means (not shown)allows rotation of the convex face 522 with resistance through adiscrete number of indent or stop positions. Convex face 522 can alsocontinuously rotate on a frictional fit with stem 545, on threadingexiting on stem 545 or by means of other well known rotation attachmenttechniques, such as a ball and socket joint. As a result of suchrotation, the angle that convex face 522 makes with the hot surface 599can be adjusted to suit the height of the intended observer.

Although FIG. 19 has been presented with device being in the shape shownin FIG. 16A, the embodiment of FIG. 19 can also accommodate othersoverall shapes of device 500, such as that shown at designation 200 inFIG. 15.

In an alternate embodiment shown in FIG. 21, clear convex cap 600 isaffixed to permanent magnet 602. Permanent magnet 602 is attracted to akeeper element 604 positioned on an opposite side of a non-ferromagneticpanel, such as a glass oven door 606.

Another alternate embodiment showing an additional means of attachmentto a smooth surface is shown in FIGS. 22A, 22B, in a device generallylabeled 605. The well known principle of a suction-cup is applied.Flexible heat resistant elastomer 608 is shown in an undeformed positionin FIG. 22A. It is to be understood that this figure is symmetric withrespect to rotation, so that the elastomer forms a circular disk.Inserted through a center of the disk and permanently bonded to it is aheat conductive stem element 610, which is further bonded to a clearconvex cap 612. In FIG. 22B, the elastomer 608 is shown in a deformedposition following a pressing of the assembly 601 against a smoothsurface 614 by a user. As is generally understood, deformation of theelastomer results in a partial vacuum formed in void space V defined bythe elastomeric disk and surface 614. This partial vacuum holds assembly601 and in particular stem 610 tightly against surface 614, forming agood thermal contact.

It will be understood that the various methods of attachment may becombined. The stem element of FIG. 22A may also be a permanent magnet,and may optionally be provided with a keeper element, as shown in FIG.21. Thereby the power of the suction cup may be augmented both forferromagnetic and non-magnetic surfaces. In other embodiments (notshown) the invention will have a protrusion from the stem, such as athreaded bolt end, passing through a penetration of a sheet of materialhaving a potentially hot surface, and engaging a fastener on a far sideof such material, such as a nut and lock washer. In yet otherembodiments such a protrusion may engage a permanently mounted springclip or fixture on an appliance, such that the hot warning button isreadily repositionable or replaceable.

As mentioned previously, FIGS. 23A, 23B, 23C illustrate geometricalconcepts mentioned in the specification. A smooth surface S has anabstract normal or perpendicular line N, as shown in FIG. 22A. Ingeneral a circularly symmetric warning device affixed to surface S (notshown) will usefully visible through a cone or solid angle C defined byan angle α. To increase the useful range of visibility a device may bemodified optically to be visible through a larger angle α', as shown inFIG. 22B, and such as is achieved by the surface convexity of theembodiments of FIGS. 15A-9, 21-22B. To enhance visibility in a givendirection, the device may be mounted at a tilt with respect to thesurface normal N as defined by axis T and angle β, as shown in FIG. 23C,and realized by the adjustably tiltable embodiment of FIG. 19. Theimprovements shown in FIGS. 23B and 23C can be combined in one device,as also illustrated by the embodiment of FIG. 19. Furthermore, thetiltable joint of the embodiment of FIG. 19 may be combined with any ofthe remaining embodiments of the invention. For example, by insertion ofa stem between permanent magnet 602 and convex cap 600 in the embodimentof FIG. 21 sufficient clearance may be gained to insert a tiltable jointin accordance with the embodiment of FIG. 19.

FIGS. 24, 25, and 26 show critical lines-of-sight in establishingsubstantial visibility of the display of three different geometricembodiments, to illustrate the principles involved.

FIG. 24 shows a rivet-shaped embodiment with an approximately sphericalor slightly paraboloid convex cap 700 of major diameter of approximate1⅛″ at the apex, where the cap is intersected by a central normal lineN, and mounted on a stem or attachment pieces 701. (A paraboloid is asolid figure formed by rotating a parabola about its axis of symmetry.Significantly with respect to the present invention a paraboloid has theproperty that it does not have a constant radius of curvature, butbecomes flatter away from the apex). Broken lines 702, 704 define theboundaries of a grazing line of sight of an observer 0. The lines aredefined as follows: line 702 is aligned with a lower face 706 of cap700, whereas line 704 is defined by geometric construction as parallelto line 702, and intersecting a surface 710 of the cap 700 at an angle γof 70°, which is considered the angular limit of useful visibility of asurface display. Therefore all lines parallel to and lying between lines702 and 704 intersect the surface of the cap at angles less than 70°.Further the perpendicular distance between lines 702 and 704 is found tobe approximately {fraction (5/16)}″, or greater than ¼″. Therefore thesurface of cap 700 meets these two conditions for substantialvisibility, as previously defined, at a grazing line-of-sight. Thesurface also necessarily meets these two conditions for substantialvisibility at a normal line of sight (not shown), parallel to line N,and at all lines of sight lying between the normal line of sight and thegrazing line of sight.

Therefore a pattern or indication (not shown) on the surface of cap 700is potentially substantially visible through a complete hemisphericalsolid angle of 180°, or angle of incidence of 90°, improving thevisibility over flat displays of the prior art, which are invisible ator near grazing angles of sight.

A similar construction is shown for a shallower cap 720 in FIG. 25,mounted on a stem 721. The cap 720 is a section of a sphere of majorradius 3″, and a rear face 722 of diameter 2″. Line N is again shown asa central normal to surface 724 of cap 720, and a construction similarto that of FIG. 24 is made for an observer O at a grazing line-of-sight.It is found once again that a width between lines 726 and 728 isapproximately {fraction (5/16)}″, and that therefore the above mentionedconditions for substantial visibility of a surface display arepotentially met for all observers in a full hemispherical solid angle:the shallower shape of cap 720 relative to cap 700 is partially offsetby its greater diameter.

A somewhat different situation is illustrated for the embodiment ofFIGS. 20A and 20B, in FIG. 26. In this embodiment a disk shaped cap 740mounted on a stem 742 has a flat front face 744 and a circumferential orcylindrical face 746. Provided that a thickness of disk shaped cap 740is greater than ¼″, in the illustration, considered to be approximately{fraction (5/16)}″, the two above considered conditions for substantialvisibility of a surface display are clearly potentially met for agrazing line-of-sight of a display on the circumferential face 746. Thecritical line-of-sight is therefore not one parallel to front face 744,but one deviating at an angle of 70° from a normal N to the front face.This is because at shallower angles of view the front face itself, hereconsidered to have a diameter of approximate 2″, will meet the aboveconsidered conditions for substantial visibility. Beyond this angle thefront face does not meet the above conditions, which therefore must bemet by the circumferential face 746 if substantially visibility is to bemaintained.

It is found by direct construction that the distance subtended by face746, or a perpendicular separation between lines 748 and 750, is greaterthan ¼″. Since a larger distance will be subtended by face 746 in alllines of sight at greater angles from normal N, and at least up tograzing line-of-sight, a display on faces 744 and 746 together of thedevice of FIG. 26 is again found to be potentially substantially visiblethrough a full 180° or hemispherical range of line-of-sight. It will beappreciated by those skilled in the mathematical arts that faces 744 and746 taken together may be described as a single “convex face”, that is,meet the mathematical definition of convexity. Therefore this case isunderstood to be covered by the language “convex face” in claiming theinvention.

It is to be understood that the dimensions given in FIGS. 24, 25 and 26are to be regarded as approximate, and intended to illustrate thegeometrical concepts only rather than be relied upon as precisedimensions of a particular embodiment.

FIGS. 27A, 27B, 27C and 27D are all alternative embodiments of thedevice of the present invention having a convex face. That is, they arealternatives to FIG. 15A. They have the same front view as FIG. 15B.They essentially consist of two parts, a container 340 and an attachmentelement 320. FIGS. 27A and 27B also have stem 345 which can be viewed aspart of container 340 or as a separate part, whichever is moreconvenient. Stem 345 offsets container 340 from the hot surface and thismakes it easier to grasp device 10. In these figures, thermochromiccomposition has become invisible since the triggering temperature hasbeen exceed (and continues to be exceeded) and thermochromic compositionhoused by container 340 reveals heat warning symbol 230A beneath saidthermochromic composition, readily visible through convex face 346.

Finally, it should be that any lines within the letters “HOT” of FIG.27C are merely intended to be one way of denoting the existence ofcolored lettering.

In general, it is to be understood that while the apparatus of thisinvention have been described and illustrated in detail, theabove-described embodiments are simply illustrative of the principles ofthe invention. It is to be understood also that various othermodifications and changes may be devised by those skilled in the artwhich will embody the principles of the invention and fall within thespirit and scope thereof. It is not desired to limit the invention tothe exact construction and operation shown and described. The spirit andscope of this invention are limited only by the spirit and scope of thefollowing claims.

1. A heat alert safety device attachable to a surface for warningindividuals that the surface is hot, comprising: a thermochromiccomposition, a container for housing said composition and having aconvex face, said face overlying said composition and said containerbeing transparent in at least a portion of the container overlying thethermochromic composition, said container made of a heat conductivematerial, the thermochromic composition designed to undergo and maintaina readily perceptible color change whenever the temperature of the hotsurface exceeds a predetermined temperature, said color change revealinga heat warning symbol that communicates that the surface is dangerouslyhot, an attachment element made of a heat conductive material and bondedto said container, said attachment element being attachable to a surfacewhich may become hot, the convex face being substantially visiblethrough an angle of incidence of at least 90 degrees, the container andthe attachment element together forming a circular shape.
 2. The deviceof claim 1, wherein said attachment element is a magnet.
 3. The deviceof claim 1, wherein when the temperature of the surface does not exceedthe predetermined temperature the thermochromic composition is ofapproximately the same color as a background color of the hot surface.4. The device of claim 1, wherein a stem is mounted between saidcontainer and said attachment element, said stem made of heat conductingmaterial and designed to offset the container from said surface andwherein the container, stem and attachment element together form acircular shape.
 5. The device of claim 4, wherein a pivot element isformed at a junction of said container and said stem, said pivot elementenabling the container to be positioned by a user in a range of angleswith respect to said surface, in order to vary a zone of maximum viewingeffectiveness.
 6. The device of claim 1, wherein a pivot element isformed at a junction of said container and said attachment element, saidpivot element enabling the container to be positioned by a user in arange of angles with respect to said surface, in order to vary a zone ofmaximum viewing effectiveness.
 7. The device of claim 1, wherein saidattachment element is a high temperature thermally conductive cement. 8.The device of claim 1, wherein said attachment element is a suction cup.9. The device of claim 1, wherein the convex face is further coveredwith a transparent vitreous coating.
 10. The device of claim 1, whereinthe thermochromic composition is a semiconductor.